In recent years, laser display devices using laser lights as light sources have been brought to attention as high-luminance laser display devices taking advantage of monochromaticity and high luminance of laser lights and having wide color reproduction ranges.
However, measures for the safety of eyes, for example, by devising the construction of an optical system for introducing a laser light as a light source to a screen are necessary in the case of a laser display device having such excellent properties. It is also necessary to reduce speckle noise produced due to high monochromaticity of laser lights.
There has been illustrated a projection type image display device constructed to be able to ensure the safety of eyes and brighten display images (see, for example, patent literature 1). This projection type image display device includes a projector means for projecting an image on a screen for image display by scanning laser lights, wherein the laser lights includes a plurality of laser beams R1 (red laser 1), G (green laser), B (blue laser) and R2 (red laser 2). These plurality of laser beams R1, G, B and R2 are irradiated with time differences substantially to the same positions of the screen by the projector means of the display device, and the safety of eyes is ensured by reducing the intensities of the laser beams projected substantially to the same positions. Further, image signals to be applied to the respective laser beams R1, G, B and R2 have time differences in conformity with the time differences of irradiation so that the preceding laser beam delays relative to the succeeding laser beam. By doing so, the intensities of the laser beams irradiated to the substantially same positions are increased to normal intensities within a specified time range, whereby a displayed image is brightened.
There has been also disclosed an example in which scanned beams of light LR (red laser light), LG (green laser light), LB (blue laser light) respectively have intensities equal to or below a specified value and have spatial intervals of a specified distance or longer from each other in any of planes at an observer side, whereby the safety of eyes is ensured (see, for example, patent literature 2). By doing so, a plurality of beams of light are prevented from being concentrated substantially at same positions to ensure the safety of eyes.
However, in the above conventional image display device or image display method, the construction of the optical system to ensure the safety of eyes and the like are disclosed, but a construction or a method for simultaneously solving the problem of speckle noise produced upon using a laser light is not disclosed. Further, there is clearly disclosed no specific solution for problems concerning the ensuring of the safety of eyes and the reduction of speckle noise in the case where a screen is arranged at an arbitrary position.
Patent Literature 1:
Japanese Unexamined Patent Publication No. 2005-31529
Patent Literature 2:
Japanese Unexamined Patent Publication No. 2005-10616